The specific alterations which occur in the control of cell proliferation in chemically transformed cells will be explored in this project. Data obtained in this laboratory using the nontransformed AKR-2B and C3H/10T1/2 mouse embryo derived cell lines and the chemically transformed derivatives of these cells, called AKR-MCA and C3H/MCA-58, respectively, have indicated that most of the characteristics of the transformed cells could be accounted for by continuous mitogenic stimulation with a growth factor. Both of the nontransformed cells have epidermal growth factor (EGF) receptors and are stimulated to proliferate by EGF. The transformed cells are not stimulated by EGF and have no detectable EGF receptors. Preliminary studies indicate that the AKR-MCA cells secrete a factor (or factors) into serum free medium which stimulates cell proliferation in the resting nontransformed AKR-2B cells and which competes for EGF binding on these cells. The studies in this project are designed to test the hypothesis that autostimulation of cells by growth factor which they themselves produce may be one mechanism in the chemical transformation of cells. This will be accomplished through the identification and attempted purification of growth factor-like substances produced by the chemically transformed cells (AKR-MCA and C3H/MCA-58) and not by the nontransformed cells (AKR-2B and C3H/10T1/2). Partially purified or "purified" growth factor will be charcterized with respect to its biological and chemical properties. Changes in the EGF receptors of nontransformed cells at various stages of the cell cycle and with continuous mitogenic stimulation with growth factors that do not compete for this receptor will be examined. It will also be determined whether the inability of the chemically transformed cells to bind 125I-EGF is due to occupancy of the receptor by a secreted growth factor, masking of the receptor by other cell constituents or rapid inactivation (down regulation) of receptor. The proposed experiments should yield data valuable in proving or disproving the hypothesis.